1. Field of the Invention
The present invention relates to a travel safety system for a vehicle, which is designed to prevent a vehicle from coming into contact with an on-coming vehicle by use of an object detecting means such as a radar device.
2. Description of the Related Art
Such travel safety systems for vehicles are already known from Japanese Patent Application Laid-open Nos. 7-262497 and 7-14100.
The system described in Japanese Patent Application Laid-open No. 7-262497 is designed, so that a locus of movement for the vehicle from the present time to a time point after the lapse of a given period of time and a vehicle position on the locus of movement are estimated, while a locus of movement for another vehicle traveling ahead of the vehicle (which will be referred to as a preceding vehicle hereinafter) from the present time to the time point after the lapse of a given time period and a preceding vehicle position on the locus of movement are estimated by the radar device, and the presence or absence of the possibility of collision is determined by comparing the vehicle position with the preceding vehicle position.
However, the above known system suffers from the following problem: It is necessary to continuously detect the current position and the current speed of the preceding vehicle in order to estimate a future position of the preceding vehicle, and for this reason, it is impossible to immediately determine the presence or absence of a possibility of collision at a time point when the preceding vehicle is detected by the radar device. On the other hand, in a case of a frontal collision which occurs when the vehicle and the preceding vehicle approach each other, there is not sufficient time from the time point of detection of the preceding vehicle until the vehicle will collide with the preceding vehicle. For this reason, in a system in which a predetermined period of time is required for determining the presence or absence of the possibility of collision as in the known system, there is the possibility that an operation for avoiding the collision of the vehicle with the preceding vehicle could not be in time for the avoidance of the collision.
The system described in the above Japanese Patent Application Laid-open No. 7-14100 is designed, so that an on-coming vehicle is detected by an object detecting means; a degree of danger of collision between a vehicle and the on-coming vehicle is estimated from the vehicle speed of the vehicle, the vehicle speed of the on-coming vehicle, the relative speed between the vehicle and the on-coming vehicle, the distance between the vehicle and a center line, the azimuth angle of movement of the vehicle and the like; and when the degree of danger of collision is equal to or larger than a predetermined reference value, a warning or an automatic deceleration of the vehicle is carried out.
The above known system is premised on the vehicle and the on-coming vehicle traveling on a straight road. For this reason, the above known system suffers from the following problem: When the vehicle and the on-coming vehicle are approaching each other while turning on a curved road or the like, the degree of danger of collision cannot be presumed precisely and hence, the avoidance of the collision cannot be performed properly.
In addition, the system described in the above Japanese Patent Application Laid-open No. 7-14100 is not designed to automatically steer the steering device of the vehicle in order to avoid the collision of the vehicle with the on-coming vehicle. For this reason, it can be considered that when a steering operation for avoiding the collision is spontaneously carried out by the vehicle driver, or when a collision avoiding operation is not carried out in the on-coming vehicle, the collision cannot be avoided, even if the vehicle is stopped by an automatic braking operation. Therefore, it can be conceived that a steering device in the vehicle is automatically steered in order to avoid the collision. However, if the timing of starting the automatic steering operation is hastened, or the steering amount in the automatic steering operation is increased in order to increase the collision avoiding effect, there is the possibility of interference with the spontaneous collision avoiding operation conducted by the driver. Further, if the variation in vehicle behavior has been already produced in the vehicle when the steering device in the vehicle is automatically steered in order to avoid the collision, there is the possibility that the variation in vehicle behavior caused by the automatic steering operation could be added to the above-described variation to produce an undesirable variation in vehicle behavior, thereby exerting an influence to the subsequent driver's driving operation.